(1) Field of the Invention
The present invention relates to novel carboxy-methyl cellulose (carboxymethyl cellulose will be hereinafter referred to as "CMC" for brevity), and a process for the preparation thereof. Furthermore, the present invention relates to a CMC structure excellent in processability and handling property, which is prepared from this novel CMC.
(2) Description of the Prior Art
Ordinary available CMC is prepared from natural cellulose (cellulose having a crystal form of cellulose I) such as linter or pulp as the starting material. Up until now, regenerated cellulose (cellulose having a crystal form of cellulose II) has not been used for the starting material of ordinary available CMC. There are two reasons for this. First, CMC can be easily prepared from natural pulp or linter. (Natural pulp or linter is prepared by removing foreign substances from a crude material such as wood or cotton linter and is available at reasonable cost.) It is therefore unreasonable economically to use, as the starting material, cellulose II obtained by further processing such natural cellulose. Second, there can be mentioned the state of the cellulose industry which has been established based on empirical facts and therefore there is a low level of understanding of the nature of cellulose chemistry or science. For example, the technique of mercerization (alkali cellulose formation) was already known in the 1870's. While it has been applied to modification of cotton fabrics for imparting silk-like luster to them, however, it has not been applied to modification of regenerated cellulose fibers. Yet regenerated cellulose fibers were already developed and marketed about 30 years after the establishment of the mercerization technique. The reason for this is that regenerated cellulose fibers are already similar to natural silk fibers, it was so true that application of mercerization was not considered necessary. In cellulose industry, it was only about 10 years ago that the fact the structure of alkali cellulose from cellulose I is different from the structure of alkali cellulose from cellulose II was accepted. Therefore, the cellulose industry does not have the scientific expertise for discriminating the differences in properties among cellulose derivatives obtained by the heterogeneous reaction from cellulose I and cellulose II, through alkali celluloses.
Most of ordinary available CMC has a total degree of substitution (hereinafter referred to as "&lt;&lt;F&gt;&gt;" for brevity) of the water-soluble region. Only CMC used as an ion exchange resin has a &lt;&lt;F&gt;&gt;of the water-insoluble region. A bench-scale method in which cellulose in the form of a fabric is converted to CMC to improve dyeability has been reported, but this research is directed to cotton alone. No literature proposes application of this method to regenerated cellulose.
The processes for preparing CMC from natural cellulose can be roughly divided into a water medium method and a solvent medium method. These methods are characterized in that in order to increase the permeability of reactants, natural cellulose is converted to alkali cellulose and then the alkali cellulose is reacted with monochloroacetic acid or sodium monochloroacetate. Furthermore, in order to control occurrence of a side reaction by monochloroacetic acid or sodium monochloroacetate, such means as mechanical pulverization, compression, shearing or stirring is customarily adopted so as to sufficiently mix starting cellulose with a reactant solution. Accordingly, CMC is obtained ordinarily in the form of a powder or ultra-fine fiber. Since CMC is ordinarily used in fields where the emulsion stabilizing effect or thickening effect is utilized, CMC is used ordinarily in the powdery form. It is pointed out that the probability of substitution at the C.sub.2 position in the glucose ring of commercial CMC is very large see, for example, Alain Parfondry et al, Carbohydrate Research, 57 (1977), 39-40 .
Since three substitutable OH groups (at C.sub.2, C.sub.3 and C.sub.6 positions) are present in the glucose ring of cellulose, it is obvious that properties of cellulose vary depending upon the probability of substitution [&lt;&lt;f.sub.k &gt;&gt;(k=2, 3, 6)] at the respective positions. This &lt;&lt;f.sub.k &gt;&gt; naturally differs according to the method for the preparation of a cellulose derivative and the kind of the starting cellulose used. Moreover, the difference of the starting cellulose results in not only a difference of &lt;&lt;f.sub.k &gt;&gt; but also a difference of the internal structure. Accordingly, there is a possibility that commercial cellulose derivatives called by general names such as CMC, methyl cellulose, ethyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose nitrate, hydroxypropyl cellulose, hydroxyethyl cellulose and ethylhydroxyethyl cellulose will be converted to derivatives having novel structures and properties.